Testing apparatus



Jul zl, 1925. 1.546.392

R. G M'CURDY TESTING APPARATUS Filed June 10, 1920 KNVBNTDR z ATTORDEY of which may be gra Patented Jul: 21, 1925.

UNITED STATES PA'TENT OFFICE.

RALPH G. HOGURDY, OF CRESSKILL, NEW JERSEY, 88161703 T0 m6 PHONE AND TELEGRAPH COMPANY, A

conrom'non or NEW You name mm'rus. Application m m. :10, 1920. Serial llo. same.

To all whom it may concern."

Be it known that I, RALPH G. MOCURDY,

residing at Cresskill, in the county of Bergen and State of New J ersey, have invented certain Im rovements in Testing Apparatus, of whicht e following is a specification.

I This invention relatesto testing apparatus and is concerned particularly with methods of and means for detecting the presence on series lighting circuits of transformers having open circuited secondaries.

such circuits, the lamps are connected to the secondaries of individual transformers whose primaries are connected in series with each other. When the filament of a lamp burns out, the current of thelighting circuit causes over-saturation of the core of the transformer. This brings about a distortion of-the voltage and current waves, in other words, the introduction of frequencies which are oddmultiples of the fundamental frequency. The present invention provides an arrangementwhereby the presence of the higher frequencies in the. lighting circuit is shown by'an indicatin instrument, the scale uated in terms of the number of lamps burned out. The indicating instrument is rendered nonresponsive to the fundamental frequency by means of a frequency selective device.

A good understanding of the invention ma now be had from the following description thereof, havin reference to the accompanying drawing s owing in diagrammatic view one form and arrangement of circuits embodying the invention.

In this drawing, reference character 1 designates a generator which supplies current to a series lightin constant current trans ormer T. The lamps L of the lighting circuit are associated with individual auto-transformers A, the rimary windings of which are connected in series with each other in circuit S.

When the filament of a lamp burns out, it opens the secondary circuit of the corresponding auto-transformer, so that the magneto-motive force due to the secondary current is extinguished. The magneto-motive force due to the primalziy current, therefore, being no longer 0 pose by that due to the seconda ration o the transformer core and can thus, a distortion in the current and voltage waves, which results in the introduction of flux between the circuit S, through a current rlngs about an over satu- "due to currents inducedupper harmonics. Owing'to the leaka of movable secondary coifind the stationary rima one of transformer T, the flow o the harmonic currents is largely prevented and hence a comparatively large difference in potential consisting of the 0d multiples of the fundamental frequency is created between the former T. This measured by connecting across theterminals of transformer Ta potential transformer P, the secondary winding of which is associated with a meter M. An im edance network N is interposed between t e meter and the transformer, this network being selective as to frequency and arranged to substantiall prevent the passage of current of the fun amental frequency into the meter, but to permit the flow therethrough of the upper harmonics. With all the lamps burning,

terminals of transtherefore, the meter indication is substantiallyzero, but with one or more filaments burned out, the'meter is actuated by current of a value d pendent on the number of open secondariesl It has been found that for any particular lighting circuit the meter scale may be so calibrated as to indicate with a high degree of accuracy the number of lamps on the circuit having burned out filaments.

In the specific form of embodiment of the invention lllustrated herein, the network is a so c'alled high-pass filter, being composed of condensers. 2 and 2 in series, inductances 3 and 3' beingbridged across thecircuit as shown Sucha filter is described fully in patent to Campbell, 1,227 ,114, dated Ma 22, 1917, and is one which will suppress al currents of frequencies below a certain value and will am or offer very low impedance to all currents of frequencies above that value.

It has been found that for a lighting circuit whose fundamental frequency 1s .60 cycles, very accurate results are obtained by means ofi a meter of 230 ohms resistance when each condenser is 2.3 microfarads, and each inductance, 0.123 henries. The invention is not limited however to the use of theparticular network illustrated it being understood that other suitable frequency selective devices may be emplo ed.

An important application of 'the recent invention is in connection with the e imina-' tion of interference in telephone circuits,

theremfrom tential difierencev is mental wave of voltage and current in the lighting circuit is generally of 60 cycles and, therefore of too low a frequency to cause an audible disturbance in the telephone circuit. However, when there is a transformer on the circuit with an open secondary, it generates harmonics of frequencies in the audible range as explained hereinbefore, which harmonics cause noise in the telephone circuit. This invention furnishes a means of detecting the presence of such transformer or transformers in the lighting circuit, so that the burned-out lamp or lamps may be replaced. re

Although I have herein shown and described only one form and arrangement of apparatus embodying the invention-and only one typesof method of practicing the same, it is readily understood that-various changes and modifications niay be made therein within the scope of the following claims withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. The method of determining the presence of a transformer with an open circuited secondary in a circuit, which consists in ascertaining the presence in the circuit of energy of higher than fundamental frequencg.

. 2. he method of determining the number' of transformers with open circuited secondaries in a series circuit, which consists in measuring the voltage of harmonics of the fundamental frequency in said c rcuit.

3. In a circuit comprising a source of current of fundamental frequency and a transformer having its primary in the circuit, means for determining the presence of an, open circuited secondary of said transformer, consisting of a device associated with said circuit for indicating the presence of current of higher thanfundamental frequenc therein. i

4. n-comb 1nation, a circuit comprising a plurality of transformers having their primaries 1n series with each other, a source of current of fundamental frequency in said circuit, a current-indicating instrument associated with said circuit andresponsive only to frequencies higher than said fundamental.

5. In combination, a circuit comprising a plurality of transformers having their primaries'in series with each other, a source of current of fundamental frequency for said circuit, a constant current transformer interposed between said source andsaid circuit, a current-indicating instrument associated with the terminals of the said transformer, and means interposed between said instrument and said transformer for rendering the said instrument substantially non-responsive to said fundamental frequency but responsive to frequencies higher than said fundamental.

6. In a device for determining the presence of a transformer with an open circuited secondary in a circuit comprising a plurality of said transformers having their primaries connected in series with each other .and supplied with current of fundamental frequency by a source associated with the circuit by means of a transformer having a large impedance, a measuring instrument associated with the terminals of the sald last mentioned transformer, and a network.

mental frequency but to substantially prevent the .flow thereinto of current of fundamental frequency.

7. The device of claim 6, in which the network of impedances comprises a capacity reactance in series path and an inductive reactance 1n shunt path.

In testimony whereof, I have signed my' name to this specification this 9th day of June, 1920. v RALPH G. MOCURDY. 

